Cells and Cell Processes

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Development of the Microscope

The light microscope can magnify up to x1000 and uses a beam of light

The electron microsope uses a beam of electrons and this allows greater magnifications of up to x50,000,000

The confocal laser scanning microsopy uses lasers to build up an image via a computer by scanning an object in the microscope. It's aim is to produce clearer images

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The Cell Theory

1. All living organisms are composed of one or more cells

2. The cell is the basic 'unit' of life

3. Cells are formed from pre-existing cells during cell divison

4. Energy flow occurs within the cells

5. DNA is passed on from cell to cell when cell divison occurs

6. All cells have the same basic chemical composition

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Micro-organisms

Micro-organisms are microscopic life forms. They include bacteria, viruses, fungi and unicellular algae.

Viruses are the smallest forms of life, and are so simple that it is not certain they can be classed as living things.They consists of some genetic material inside the protein case. They can only reproduce inside another living cell, the 'host' cell. The release of the new viruses the attack the new host cells.

Bacteria reproduce asexually by dividing into two.

Yeasts are microscopic fungi. They reproduce asexually by budding - growing a new cell from an existing one, after which the new cell breaks off.

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Structure of Proteins

One of the most important groups of proteins. Enzymes control all the chemical reactions which occur in cells.

Proteins are made of a chain of smaller molecules called amino acids. The sequence of the amino acids gives the protein it's identity and properties.

The shape of the enzyme molecule is essiential to the function of the enzyme

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How enzymes work

A particular enzyme will only work on one chemical or a small group of similar chemicals. The substance that an enzyme works on is called its substrate. The enzyme has to make contact with its substate and attach to it. 

The place on the enzyme where the substrate attaches is callled the active site. Enzymes are specific because the substrate shape has to match the shape of the active site.

When the enzyme and substate are locked together , the combined structure is called an ezyme -substate complex.

This is called the lock and key theory.

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Properties of Enzymes

Enzymes are biological catalysts.

Each enzyme has its own optimum pH and temperature

Enzymes are denatured by high temperatures, because the heat breaks the chemical bonds that hold the enzymes active site in shape. All enzymes are denatured by boiling.

If the pH is very far from the optimum, the enzyme may be denatured.

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Uses of Enzymes

Digestive enzymes are lipases, proteases and carbohydrases. These are put into the detergents to catalyse the breakdown of the stains that are otherwise difficult to remove

Lipids are broken down by lipases.

Proteins are broken down by proteases.

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The structure of DNA

DNA has two long chains of alternating sugar and phosphate molecules

The two chains are twisted into a shape called a double helix, which is an interlocking spiral.

These chains are joined by bases

There are four bases; adenine (A), cytosine (C), guanine (G) and thymine (T)

The order in which these bases occur along the chain forms a 'code', which determines the order in which different amino acids are linked together to form different proteins

Adenine A always joins with Thymine T

Cytosine C always joins with Guanine G

It is a sequence of three bases along the DNA chain whiich 'codes'for each amino acid. This is called a triplet code.

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The Importance of DNA

DNA is short for Deoxyribrose nucleic acid.

It is the chemical which provides 'instructions' for every cell to work. 

Enzymes are proteins which control all the chemical reactions of life. 

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Mitosis

The most common form of cell division is called mitosis. This produces new cells for growth, for repair of tissues and to replace worn out cells. 

Mitosis takes place in all tissues of the plant and animal body, execpt those that form sex cells 

It provides cell for growth, repairs and for the replacement of old cells

Two new daughter cells are formed.

Each of the new cells has a full set of chromosomes 

The new cells are genetically identical to each other and to the mother cell

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Meiosis

When gametes are formed a different type of divison, meiosis, takes place.

Meisosi only takes place in tissues which form sex cells/gametes.

Four cells are formed, because meiosisis a double divison

Each of the daughter cells has half a set of chromosomes. The chromosome numbers are halved in the first two divisions

Each of the new cells is genetically different

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